The issue was the file being large (5gb). After saving it and closing then opening it again, it took several minutes for the program to get responsive then it worked. It appears hitfilm has to process it before audio works.

The 5GB file size might not necessarily be the issue. I use files that large all the time, but they've been transcoded to make it easier to edit in HitFilm, and there's very little delay when importing them. It's more likely the combination of codec and bit rate used to compress the data in the file. For example, even though HitFilm can technically use variable bit rate (VBR) files, there are still issues that crop up. VBR is great for playback, but not so great for editing.

If you haven't already done so, check out this video that talks about the ins and outs of transcoding, which is a very useful step before you drop footage into HitFilm (or any editor):

@jsbarrett I think you meant to say variable frame rate and not variable bitrate. Variable bitrate should never a problem.

@lelcat Hitfilm does process the audio on import IF the sample rate is different than the project rate. Hitfilm resamples the audio to the project sample rate and saves that in the Hitfilm cache.

If you are using really long files, therefore large, and your audio is in a compressed format you will want to turn timeline waveform display OFF. Hitfilm has waveform performance issues and compressed audio (MP3, AAC) accentuate the issue. AAC is normal/common in MP4 files. PCM audio can still work well even with large files. Anyone who transcodes to DNx/Prores or Cineform will have PCM audio.